Existing apparatus for volumetric metering, especially of the type used in the preparation of dye solutions for dyeing textile materials, comprise essentially a structure with a platform having vessels or "bottles" disposed thereon which contain the solutions. Each vessel contains one solution corresponding to a predetermined colour and being located in a fixed and preset position of the platform. Provided in a separate station of the same platform, in correspondence of fixed and preset positions, are vessels or "glasses" intended to receive the solutions drawn from the bottles in preset doses. The withdrawal and metering of the solutions are operated by means of a syringe or "pipette" movable on the platform between the bottles containing the solutions to be drawn therefrom and the glasses which receive them in preset doses. An electronic processor or computer controls the movements of the pipette between the various sites on the platform.
In order to use the same syringe upon the removal and metering of different solutions, a washing is to be carried out each time by means of a suitable solvent to avoid detrimental solutions contaminations. Such an apparatus is disclosed in the document EP-A-0,602,737.
A drawback stemming from the use of an apparatus of the type above described is the fact that whenever the syringe is washed, there is a loss of residual liquid, that is, the liquid exceeding the dose to be taken into the glasses, which residue is ejected together with the solvent and collected in a drain duct for subsequent disposal thereof along with other elements.
A further drawback lies in the general slowing down of the operations due to the time and care required to carry out a proper washing of the syringe. Besides, it is not to be fully excluded the possibility that the solutions will be contaminated all the same, since, subsequently to the washing, the syringe chamber may still exhibit some amounts of residual solvent.
It should also be noted that by using this type of apparatus for the volumetric metering of liquids such as essence and perfume solutions, each washing requires a huge quantity of solvent, or alcoholic products, which are more expensive than water. In this industrial sector, the problem of possible contamination of different solutions to be treated is in fact particularly felt, and such contaminations may bring about damages which are more serious than in the case of preparing dye solutions for dyeing textile materials.